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DPI model of SPI-connected SD card
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@alees24
alees24 committed Nov 29, 2024
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38 changes: 38 additions & 0 deletions doc/guide/sdcard-setup.md
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# Setting up SD card image for 'sdcard_tests.hh'

To set up a FAT32-formatted SD card image 'sd.img' on a Linux system, the following
may be useful:

https://github.com/procount/fat32images offers various ready-to-download volume images.
The 1GiB example (nnobs1gb.img.zip) should suffice; rename it to 'sd.img'

Find the offset of the FAT32 partition:

> fdisk -u sd.img
```
Disk sd.img: 1 GiB, 1073741824 bytes, 2097152 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x6c4676d7
Device Boot Start End Sectors Size Id Type
noobs1gb.img1 8192 2097151 2088960 1020M c W95 FAT32 (LBA)
```

Note the 'Start' value (8192) and multiply it by the sector size (512 bytes),
e.g. 4194304 in the command below:

Create a mount point within the filing system for the FAT32 partition.
> mkdir mnt_point
Make the FAT32 partition available.
> sudo mount -o loop,offset=4194304 mnt_point sd.img
Copy the lorem ipsum text (or other files) into the root directory of the FAT32 partition.
> sudo cp <lorem file> mnt_point/lorem.ips
Unmount the FAT32 partition.
> sudo umount mnt_point
318 changes: 318 additions & 0 deletions dv/dpi/spidpi/spi_microsd.cc
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// Copyright lowRISC contributors.
// Licensed under the Apache License, Version 2.0, see LICENSE for details.
// SPDX-License-Identifier: Apache-2.0

/**
* This DPI model provides a simple implementation of a SPI-connected microSD card.
* It provides enough functionality for the existing tests to run in simulation
* but little more than that.
*
* Single Block Read/Write commands are supported and the normal initialisation
* sequence.
*
* The code expects a file of the name specified to the constructor, e.g. 'sd.img',
* and will operate on that as if it were an SD card, performing block transfers
* to/from that file.
*/

#include <cstring>

#include "spi_microsd.hh"

// SD command codes.
enum {
CMD_GO_IDLE_STATE = 0,
CMD_SEND_OP_COND = 1,
CMD_SEND_IF_COND = 8,
CMD_SEND_CSD = 9,
CMD_SEND_CID = 10,
CMD_STOP_TRANSMISSION = 12,
CMD_SET_BLOCKLEN = 16,
CMD_READ_SINGLE_BLOCK = 17,
CMD_READ_MULTIPLE_BLOCK = 18,
CMD_WRITE_SINGLE_BLOCK = 24,
CMD_WRITE_MULTIPLE_BLOCK = 25,
SD_SEND_OP_COND = 41,
CMD_APP_CMD = 55,
CMD_READ_OCR = 58,
CMD_CRC_ON_OFF = 59,
};

void spi_microsd::reset() {
spidpi::reset();
cmdBytes = 0u;
responding = false;
reading = false;
writing = false;

// Initialise the CID
memset(cid, 0, sizeof(cid));
cid[15] = update_crc7(0, cid, 15);
// Initialise the CSD
memset(csd, 0, sizeof(csd));
csd[15] = update_crc7(0, csd, 15);
}

void spi_microsd::writeByte(uint8_t inByte, uint32_t oobIn) {
logText("microSD %0x\n", inByte);

if (writing) {
switch (writeState) {
case WriteState_StartToken:
if (inByte == 0xfeu) {
writeState = WriteState_DataBytes;
// CRC16 is seeded with all zero bits.
writeCrc16 = 0u;
}
break;
case WriteState_DataBytes:
if (writeBytes < sizeof(writeBuf)) {
writeBuf[writeBytes] = inByte;
}
writeCrc16 = update_crc16(writeCrc16, &inByte, 1u);
if (++writeBytes >= kBlockLen) {
writeState = WriteState_CRC0;
}
break;
case WriteState_CRC0:
if (inByte != (uint8_t)(writeCrc16 >> 8)) {
logText("Mismatched CRC16 on write data");
}
writeState = WriteState_CRC1;
break;
case WriteState_CRC1:
if (inByte != (uint8_t)writeCrc16) {
logText("Mismatched CRC16 on write data");
}
writeState = WriteState_StartToken;
// The data_response is 0xe5 indicating that the write data has been accepted,
// and then '0' bytes whilst busy until Idle again.
sendResponse(8u, ((uint64_t)0x01 << 56) | 0xe5);
writing = false;
// At this point we write out the data block.
if (sd && kBlockLen != fwrite(writeBuf, 1, kBlockLen, sd)) {
logText("Failed writing to SD card");
}
break;
default:
break;
}
} else {
switch (cmdBytes) {
case 0u:
if ((inByte & 0xc0) == 0x40) {
cmd.cmdCode = inByte & 0x3f;
cmdBytes = 1u;
}
break;
case 5u:
cmd.crc = inByte;
startCommand();
cmdBytes = 0u;
break;
default:
// Collect the next byte of the address.
cmd.address = (cmd.address << 8) | inByte;
cmdBytes++;
break;
}
}
}

bool spi_microsd::readByte(uint32_t oobIn, uint8_t &outByte, uint32_t &oobOut) {
if (responding) {
if (rspBytes < rspLen) {
outByte = rsp[rspBytes++];
// OOB data carries SD card detect - absent (1) or present (0).
oobOut = !sd;
return true;
}
if (reading) {
readState = ReadState_DataBytes;
// CRC16 is seeded with all zero bits.
readCrc16 = 0u;
}
responding = false;
}
if (reading) {
// Checksum?
switch (readState) {
case ReadState_DataBytes: {
switch (cmd.cmdCode) {
case CMD_SEND_CID:
outByte = cid[readBytes];
if (++readBytes >= sizeof(cid)) {
readState = ReadState_CmdStatus;
}
break;
case CMD_SEND_CSD:
outByte = csd[readBytes];
if (++readBytes >= sizeof(csd)) {
readState = ReadState_CmdStatus;
}
break;
case CMD_READ_MULTIPLE_BLOCK:
case CMD_READ_SINGLE_BLOCK: {
// Return the next byte from the memory.
int ch = 0xffu;
if (sd) {
ch = fgetc(sd);
if (ch == EOF) {
logText("Failed reading from SD card");
}
}
outByte = ch;
readCrc16 = update_crc16(readCrc16, &outByte, 1u);
if (!(++readBytes & (kBlockLen - 1u))) {
readState = ReadState_CRC0;
}
}
break;
default:
break;
}
}
break;
case ReadState_CRC0:
outByte = (uint8_t)(readCrc16 >> 8);
readState = ReadState_CRC1;
break;
case ReadState_CRC1:
readBytes = 0u;
outByte = (uint8_t)readCrc16;
readState = ReadState_DataBytes;
break;
default:
outByte = 0xffu;
reading = false;
break;
}

// OOB data carries SD card detect - absent (1) or present (0).
oobOut = !sd;
logText("Read byte 0x%0x\n", outByte);
return true;
} else {
return false;
}
}

// Transition on one or more CS lines.
void spi_microsd::csChanged(bool csAsserted, uint32_t oobIn) {
cmdBytes = 0u;
responding = false;
reading = false;
}

// TODO: prevent command processing trying to read from non-extant SD card;
// reject out-of-order command codes etc.
void spi_microsd::startCommand() {
logText("Starting command %02x,%08x,%02x", cmd.cmdCode, cmd.address, cmd.crc);
switch (cmd.cmdCode) {
case CMD_GO_IDLE_STATE:
sendResponse(1u, 0x01);
break;
case CMD_SEND_IF_COND:
sendResponse(5u, 0);
break;

// Card Identification Data and Card Specific Data may be handled similarly.
case CMD_SEND_CID:
case CMD_SEND_CSD:
sendResponse(1u, 0xfe);
reading = true;
readState = ReadState_CmdStatus;
readBytes = 0u;
break;

case CMD_STOP_TRANSMISSION:
break;
case CMD_SET_BLOCKLEN:
sendResponse(1u, 0);
break;
case CMD_READ_MULTIPLE_BLOCK:
case CMD_READ_SINGLE_BLOCK:
// TODO: introduce error code responses.
if (sd) {
logText("Reading from block %08x", cmd.address);
fseek(sd, cmd.address << kLog2BlockLen, SEEK_SET);
}
sendResponse(1u, 0xfe);
reading = true;
readState = ReadState_CmdStatus;
readBytes = 0u;
break;
case CMD_WRITE_MULTIPLE_BLOCK:
case CMD_WRITE_SINGLE_BLOCK:
// TODO: introduce error code responses.
if (sd) {
logText("Writing to block %08x", cmd.address);
fseek(sd, cmd.address << kLog2BlockLen, SEEK_SET);
}
sendResponse(1u, 0xfe);
writing = true;
writeState = WriteState_StartToken;
writeBytes = 0u;
break;
case SD_SEND_OP_COND:
sendResponse(1, 0x00);
break;
case CMD_APP_CMD:
sendResponse(1, 0x00);
break;
case CMD_READ_OCR:
sendResponse(5u, 0);
break;

default:
// Treat anything else as an illegal command.
sendResponse(1u, 0x05);
break;
}
}

void spi_microsd::sendResponse(unsigned len, uint64_t d) {
responding = true;
rspBytes = 0u;
rspLen = len;
rsp[0] = (uint8_t)d;
rsp[1] = (uint8_t)(d >> 8);
rsp[2] = (uint8_t)(d >> 16);
rsp[3] = (uint8_t)(d >> 24);
rsp[4] = (uint8_t)(d >> 32);
rsp[5] = (uint8_t)(d >> 40);
rsp[6] = (uint8_t)(d >> 48);
rsp[7] = (uint8_t)(d >> 56);
}

// Update the running CRC7 value for a series of bytes (command/response);
// used to generate the CRC for a command or check that of a response if CRC_ON mode is used.
//
// Note: the CRC7 is held in the MSBs of the byte, which should be set to 0 for the first
// invocation, and then the trailing LSB is always 1.
uint8_t spi_microsd::update_crc7(uint8_t crc, const uint8_t *data, size_t len) {
while (len-- > 0u) {
uint8_t d = *data++;
for (unsigned b = 0u; b < 8u; b++) {
crc = (crc << 1) ^ (((crc ^ d) & 0x80u) ? 0x12u : 0u);
d <<= 1;
}
}
// 7 MSBs contain the CRC residual and the trailing bit is 1.
return (crc | 1u);
}

// Calculate the CRC16 value for a series of bytes (data blocks);
// used for generation or checking, if CRC_ON mode is used.
//
// Note: the CRC shall be zero for the first invocation.
uint16_t spi_microsd::update_crc16(uint16_t crc, const uint8_t *data, size_t len) {
while (len-- > 0u) {
uint16_t d = (uint16_t)*data++ << 8;
for (unsigned b = 0u; b < 8u; b++) {
crc = (crc << 1) ^ (((crc ^ d) & 0x8000u) ? 0x1021u : 0u);
d <<= 1;
}
}
return crc;
}
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